Update on Vaccine-Derived Polioviruses --- Worldwide, January 2017--June 2018

Oct 25, 2018
After the 2016 synchronized switch from trivalent oral poliovirus vaccine (OPV) (types 1, 2, and 3) to bivalent OPV (types 1 and 3), transmission of type 2 circulating vaccine-derived polioviruses was detected in countries with subpopulations of children who missed immunization to type 2 poliovirus before the switch.

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